# Arithmetic Progression

1. May 29, 2015

### osirvics

1. The problem statement, all variables and given/known data
The first term of an a.p is -8, the ratio of the 7th term to the 9th term is 5:8. what is the common difference of the progression?

2. Relevant equations

3. The attempt at a solution
I've tried... it confuses me. Can anyone give me some hints or tips...?

2. May 29, 2015

### SammyS

Staff Emeritus
Hello osirvics. Welcome to PF !

In the future, you need to show your attempt at a solution.

Do you know a general formula for the nth term in an arithmetic progression ? What is that formula?

3. May 29, 2015

### osirvics

Okay, thanks.
Yes, tn = a + (n – 1) d.
but i don't know how to implement it. this statement "the ratio of the 7th term to the 9th term is 5:8" is confusing me.

4. May 29, 2015

### Staff: Mentor

Thread has been locked for your not showing any effort. Please start a new thread and fill out your Attempt at a Solution part of the HH Template. Thank you.